The present invention relates to equipment of the type used in surveying and construction, and, more particularly, to a detector device for such an application which detects the position or level of a reference plane defined by a rotating laser beam.
Laser beam systems have been employed in surveying and construction in which a laser beam is rotated in either a horizontal or graded plane. U.S. Pat. No. 4,062,634, issued Dec. 13, 1977, illustrates a laser projector device which provides such a rotating reference beam. The rotating beam defines a plane, and various measurements can be made using the plane as a reference. For example, the elevation of a point remote from the laser beam projector device may be measured by means of a rod on which a laser beam detector is mounted. The bottom of the rod rests on the ground at the point where the measurement is to be made, and the operator moves the detector along the rod to a position where it intercepts the laser beam, as indicated by a meter or other display on the detector device. One such detector device is shown in U.S. Pat. No. 4,240,208, issued Dec. 23, 1980, to Pehrson. Other construction applications for laser systems include leveling concrete forms or foundations, setting grade stakes, screeding, establishing foundation heights, and setting plumbing and drains.
Rotating laser beam systems have in the past had certain limitaions when used over relatively long distances. Although projected very precisely from the laser projector device, the beam is nevertheless subject to random disturbance by various environmental factors, such as thermal air currents. Additionally, although the projector device which provides the rotating beam is accurately positioned and aligned, it may be subjected to some slight vibration as a result of wind, which vibration produces random deflection of the beam out of its reference plane.
A detector device typically indicates whether the beam is striking the device at a reference level on the device, or whether the beam is striking the detector device above or below the reference level. When the height of the beam is fluctuating randomly, however, the detector may produce rapidly changing "high", "low" and "on" readings. As a consequence, the detector device will not provide a meaningful indication of beam height to the user under these conditions.
In one prior art system, an attempt was made to reduce fluctations in readings by requiring that a high or low indication be provided only if two such measurements are made without an intermediate measurement of opposite sign. While providing some improvement over prior art detectors, this system nevertheless retained an undesirable degree of sensitivity to random variations in beam position.
Accordingly, it is seen that there is a need for a detector for a light beam, such as a laser beam, which detects the position of the beam accurately even, though the beam is subjected to random positional disturbances.